Centrifugal pumps such as disclosed in U.S. Pat. No. 2,117,011 are provided for increasing the pressure of fluids by driving vanes carried on a rotor within a housing. As water is fed to cavities provided between adjacent vanes on the rotor, the fluid is transported to an outlet port. One problem with such pumps is that some of the fluid carried between the adjacent vanes is not discharged out of the outlet port as that particular chamber passes the outlet port affecting the efficiency of the pump. Similar centrifugal pumps are disclosed in U.S. Pat. Nos. 640,345 and 2,724,338.